In an electronic data storage and retrieval system, a magnetic recording head can include a reader portion having a sensor for retrieving magnetically encoded information stored on a magnetic medium. Magnetic flux from the surface of the medium causes rotation of the magnetization vector of a sensing layer or layers of the sensor, which in turn causes a change in the electrical properties of the sensor. The sensing layers are often called free layers, since the magnetization vectors of the sensing layers are free to rotate in response to external magnetic flux. The change in the electrical properties of the sensor may be detected by passing a current through the sensor and measuring a voltage across the sensor. Depending on the geometry of the device, the sense current may be passed in the plane (CIP) of the layers of the device or perpendicular to the plane (CPP) of the layers of the device. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover information encoded on the disc.
A structure in contemporary magnetic read heads is a thin film multilayer structure containing ferromagnetic material that exhibits some type of magnetoresistance. One magnetoresistive sensor configuration includes a multilayered structure formed of a nonmagnetic layer (such as a thin insulating barrier layer or a nonmagnetic metal) positioned between a synthetic antiferromagnet (SAF) and a ferromagnetic free layer, or between two ferromagnetic free layers. The resistance of the magnetic sensor depends on the relative orientations of the magnetization of the magnetic layers.
Magnetic read sensors have magnetic shields that to increase the spatial resolution of the read sensor by shielding the read sensor from stray magnetic fields. It is important that the magnetic domain configuration of the magnetic shield and its response to small magnetic fields from recording media be stable against exposure to large and nonuniform magnetic fields in order to minimize unwanted noise registered in the read sensor. The magnetic domain configuration can be established by controlling the magnetic anisotropy of the ferromagnetic shield material. However, processing of the read sensor can require that the shield be exposed to strong magnetic fields at elevated temperatures that can reorient (e.g., cause magnetic grain growth) the magnetic anisotropy of the magnetic shield in an unfavorable way.